Pressure-regulating valves are frequently used in a hydraulic circuit for the purpose of converting a variable primary pressure, which is often applied from a pump or a hydraulic accumulator as the pressure source to a supply connection of the valve, into a constant, reduced secondary pressure. In addition, the increase in the secondary pressure at the assignable utility connection of the regulating valve resulting from external and application-specific influences is prevented with an additional pressure release to an additional fluidic connection of the valve, commonly in the form of a tank connection or return connection. The design as a seat-tight pressure-regulating valve ensures the sealing of the connection from the primary pressure side to the regulating pressure side or from the regulating pressure side to the tank connection or return connection of the valve. In this way, once a static regulating pressure has been obtained, an increase in this pressure is prevented by the sealing relative to the primary pressure side. The reduction in pressure by the relief function commences only once a maximum pressure level is exceeded. The seat-tight construction of a pressure-regulative valve differs from the slide construction, in which the opening cross sections of the through-flow directions are obtained by the axial displacement of a valve piston in a valve body provided with radial bores.
One example of this type of pressure-regulating valve is disclosed in EP 1 970 787 B1. This known pressure-regulating seat valve for hydraulic systems, in particular for machine tool clamping devices, is provided with a main seat arranged between a supply pressure connection and a regulating pressure connection in the form of a utility connection. An upstream spring-loaded main closure element is assigned to the utility connection, for the purpose of setting the regulating pressure by the main seat, and can be mechanically loaded by a regulating piston that, downstream of the seat, is loaded by the regulating pressure against a regulating spring. Because in the known solution a discharge valve with a seat valve construction is arranged in a flow path between the regulating pressure connection and a discharge connection or tank connection, which discharge valve can be mechanically controlled to the discharge connection when the regulating pressure set by the regulating spring is exceeded until such time as the regulating pressure is restored, and because the activation of both the discharge valve and of the main closure element can be set by the regulating spring, a three-way pressure-regulating seat valve is realized. This valve requires only a single setting opportunity for the regulating pressure setting, namely, for the preloading of the regulating spring. This advantage is achieved in particular by the integration of the flow path to the discharge connection and of the discharge valve with a seat valve construction into the flow path, and with the single regulating spring that acts both for the discharge valve and the main seat valve.